How to stretch selected vertices to mathfunction or bezier
What you want can be done in a number of manners, but most of them are retopology tools:

RetopoMT by Blenderlounge:

https://youtu.be/op2rMKDEUzQ?t=566

SpeedRetopo by Cedric Lepiller

https://youtu.be/BFfqePn8nKI?t=21

https://youtu.be/NdbBX957JYo?t=286

Retopoflow by cgcookie:

https://www.youtube.com/watch?v=9qidVmJjtBA

Bsurfaces:

https://youtu.be/3VC98kiy10Q?t=117

https://www.youtube.com/watch?v=mptQWDbKhW0

Mira Tools for editing loops as curves:

https://www.youtube.com/watch?v=iO4OjsqJpxQ

Curve Tools for nurbs modeling:

https://blenderartists.org/forum/showthread.php?221213-Tools-for-curves

Also, on the same LoopTools addon that you use, there are options on the W menu for relaxing and spacing of the vertices, they may be useful in your case.